A flow control valve of a construction equipment as shown in FIG. 1 according to the conventional technology has a valve body (2) installed on the path between a hydraulic pump (not shown) and a hydraulic actuator (1). A switchable spool (3) is provided within the valve body (2) so that by switching, a hydraulic oil of the hydraulic pump can be supplied to the hydraulic actuator (1) and a hydraulic oil discharged from the hydraulic actuator (1) can return to a hydraulic oil tank (not shown).
Within the valve body (2) are provided a pump path (4) supplying the hydraulic oil from the hydraulic pump, a supply path (5) communicating with the pump path (4) and the actuator ports (6, 7) connected to the hydraulic actuator (1).
In the flow control valve as describe above, the spool (3) is shifted to the left side in the figure when the pilot signal pressure is applied in the right side of the spool (3). At this time, a check valve (11) is moved upwards in the figure and opened by the hydraulic oil supplied to the pump path (4) from the hydraulic pump.
Accordingly, the hydraulic oil supplied to the pump path (4) is delivered to the hydraulic actuator (1) by way of the supply path (5), a spool notch (8), and the actuator port (6) in order. At the same time, the hydraulic oil discharged from the hydraulic actuator (1) returns to the hydraulic oil tank by way of the actuator port (7), a spool notch (9), and a tank path (10) in order. Thus, the hydraulic actuator (1) is actuated in contraction.
If the hydraulic actuator (1) is the boom cylinder that makes the boom up and down, the boom cylinder is actuated in contraction due to the weight of the boom itself before the bucket digs into the ground, even though the hydraulic oil is not supplied to the small chamber of the cylinder. Therefore, the contraction of the boom cylinder makes the hydraulic oil supplied to the small chamber unnecessary, which otherwise causes the problem of lowering the fuel efficiency due to the waste of the hydraulic energy.